Tatsuya is the single strongest candidate perhaps in all of anime for autism.  He is socially inept which may not be so obvious due to his other stellar qualities making him stand out so much that others tend to flock to him and try to befriend him.  But he never seems to comprehend what to do or how to behave.  Such as when he is called a 'total stiff' at the nine schools games.  He does not actually lack emotions but like people with autism, he suppresses them severely and struggles to express them or to express them appropriately.  His focus is top notch that he can remain calm even in crisis.  His 'powers' may well be a reflection of the autism way of specializing in a few topics obsessively which he does do as well by focusing in magical engineering, martial arts, and combat magic.  

Edit:  One of his key powers is basically a common autism quality albeit boosted a bit for story lore.  He has an overly sensitive pseudo radar ability which he can use to sense hostility of even just detect presences through walls.  He doesn't cheer when he earns any merits.  His facial expression rarely changes or shows any reactions.  He misreads Saigusa's affection until moments where she says something flat out.

One could say she is clearly a blood relative of Tatsuya's by displaying many of the same issues and even similar powers even if not with the same amount of energy reserves he has.  She is said to rarely leave her house if ever and most communication from the main house is done through Hayama, her butler.  Her social disfunction may well come from her trauma but even her sister displayed marked qualities and both of them had similar issues even before her trauma which at the very least made her 'autism' traits more severe.  Her best social stance is to subtly or directly order people around because she has few to no social graces.  Her focus is relagated to running the family and it's businesses. Physically she has not appeared to age for decades which according to some sources is often thought of as a common trait in autism as well.  Her level of anxiety in social settings or discomfort is high enough that she is rarely seen, but then if you knew her family and her history, you could hardly blame her.

Edit:  The show only shows a fraction of her character.  Her background suggests she was the type to throw reactivel bipolar kind of fits not unlike someone with autism in the wrong setting.  She treats people generally more like tools than sentient life forms in a way suggesting a bad history or perhaps just general lack of capability in dealing with others.  When her sister showed she wasn't much different before and after the great family tragedy, it kind of shows, it wasn't just a ptsd type of reaction but something at birth.  There are others in the family who also show degrees of autism like behavior or symptoms but not necessarily enough to show other family members have it but do prove the higher than average chance it could happen in her family if several members are already showing signs though not a full blown diagnostic case.

Leon might well have the greatest probability of having autism. He has shown some of the most classic characteristic symptoms of autism I’ve ever seen in an anime. He is a veritable genius yet has the mentality in of a child about every other respect other than his narrow field of interests. Though he can interact with other humans, he has almost no skill, understanding, or awareness in any form of said interaction. He is one of the the most obsessively over focused individuals yet seen in anime and it’s so bad that he is literally aware of NOTHING else like when his adoptive sister is talking or he walks into a tree. Sometimes he forgets even to eat which I sometimes do when I over focus. It’s hinted at least one character might have romantic interests but he never seems aware nor gets any possible hints. If not for his sister, he might well struggle to survive given how unreliable and unaware he is about essentially anything of than his research or areas of specific interests.

In many ways, she is almost like a female version of Tatsuya the way her dispassionate emotionless demeanor reflects her profusely logical mind.  She often acts more like a computer than a human as she is often running formulas or simply answering queries as if someone typed it into google.  Her face acdtually changes less than Tatsuya's and sadly in many respects she shows even less emotion than Tatsuya ever does.  Research or collecting data appears to be among her strong points that she obsesses over.

He only seems able to follow tasks precisely yet even then he can still get easily distracted from his focus if he finds something appealing to him. He is awkward socially and even so among all the girls that his behaviors often offend or confuse others as well as his ability to understand people's non verbal cues. When he does focus, nothing can disrupt or interrupt him as if he is afflicted with the same 'over focus' trait many with autism have.

Edit:  No he may not seem like a typical case, but he is oblivious to many signs, signals, and other nonNT response triggers to make one wonder.  He showed at least some hinted signs he might have hypersensitivity.  In his case, he doesn't lack social bravery, (yet there scenes where he acts very awkward or shy, his 'apparent' socializing may almost be more like an illusion or some other deception or trick) as much as the a average asdie but nearly every other symptom, he has shown at least a vague hint about.

In episode 5 alone she displayed a very typical experience socially speaking. She doesn’t know how to interact with others or express herself. Another character flat out observed that she totally doesn’t get body signals. She may or may not display many traits but the ones she does, she does so quite pronounced.

Nureha is alot like Maya Yotsuba only she shows more emotion, moves around a bit more, and hangs around more people.  But you can pretty much tell she hides within a cage even when she is outside or among others.  Like Maya, much of her communication is done through her subordinate.

Miki tends to share alot of Mizuki's traits which I suppose is part of what makes them such a good and obvious match.  He is shy, soft spoken, often quiet, and does not stand out much.  He lacks confidence in himself yet spends alot of time in private working on his interests such as spirit summoning.  When Tatsuya talks to him about it after spotting him practicing, he talks about Mizuki in a clearly inappropriate way as if she were not even there and never realizes this.  Someone with Autism can easily look back upon this and reflect that a suggestion of kidnapping someone right before them is probably not the most proper thing to say.  If you are not careful though, it is easy to miss the more subtle clues like this through out the series when looking for the many characters with Autism.

Shino is so anti social that she lives in the vr world more than the real world and spends much of her spare time in it.  It may have been caused by a trauma but even then the flashback of that event does not give great credence to the possibility that she was exactly a social butterfly either.  It maybe impossibe to say if she was like this to some grand degree already or not as we know little about her before the trauma event.  However, even after she somewhat gets over it, she is not exactly a party animal.  In games and out during her ptsd like suffering and after she somewhat emerges from it, she keeps pretty much to herself.  In game she had essentially only one friend which goes to show that her one escape she did not really bloom.  Shino has some interests in which she what one might say over focuses on such as vr, online gaming, and ranged weapons.

The first clue is the fact she constantly calls Shiroe my lord from the get go.  This essentially proves she is socially handicapped from that alone.  Her flashbacks to real life prove even more so how potent her handicaps, anxieties, and internal escapism were.  In the game world and after the game world becomes real, she might be a tad more confident and even socialable but her real self shines through strongly enough to tell us, she has some pretty apparent Autism qualities.  Her ninja interest is so strong she creates a class for that that didn't even exist in the game and spends much of the time and even free time practicing it.  The few times we see her with Shiroe trying to be amicable or with others in a non combat situation, her lack of confidence and difficulties navigating those moments become clear.  One example is when she turns to Nyanta for advice about Valentine's as if she had no clue what to do.  Another example is when she watches one of the allied groups practicing before the big Raid enemy event within the city but even after they try to invite or welcome her she remained aloof and uncertain.

If I were a body movement expert I might point out how clearly she constantly holds her arms and body inward as if she were scared to venture out into the world beyond her own home.  Mizuki is soft spoken, shy, clumsy, awkward, quiet, and often clueless to social cues such as when Tatsuya and Miki are talking about her right in front of her.  After watching just a few episodes that feature her for more than a few scenes, it is easy to see how well she fits the Autism moniker.  Despite what the author himself may or may not say about it, or even if he intended to put so many characters with autism in his show, he in effect does.  Their characteristics even if unintended quite clearly reflect an autism condition quite strongly.  Mizuki is probably one of the easier characters to see that in.

Like Mizuki, she lacks confidence and with a careful analysis you can see she often tries to make herself appear smaller, less significant, or even invisible by her subtle but distinct body motions.  You might get the feeling she is on the student council because she knew one or more of the other members and got talked into it as it is doubtful she ever had the gusto to charge into such a thing all on her own.  Like a typical person with autism, she has at least one very strong super obsession which she seems to know a little TOO MUCH about, aka Tarus Silver and every device he designed.

Shinji has a strong desire to be cool or copy off someone who is or if nothing else follow them around hoping that something of that coolness rubs off on him.  He is as meek as they come and has such little presence, you might not be aware when he is on screen.  Some of his behaviors look a bit like he needs an instruction book just to know how to say hi to others.  

His shortcomings are not only similar to some I’ve seen in real life autism cases but totally spot on, such as buying a ring but not realizing the implication. This is something the world he came from most likely had to do it’s not something strictly lacking education wise from the fantasy world. He’s blunt without holding back. He’s focused almost exclusively on specific topics of interest. He’s so focused he rarely considers consequences, benefits, or deficits fully. He essentially only knows about his favorite topics but little else so much so he struggles to understand or fit in.

Edit:  He is like Kenshi, in that he isn't as obvious or atypical of an asdie.  Yet his inability to not only comprehend his inappropriate behavior at times but sheer lack of ability to even correct it much if at all suggests something deeper.  Shin gets extremely hyper focused at times where he doesn't pay attention to anything else which is another clear flag for me.  Even when he does attempt to 'socialize' it is often done incorrectly or sends the wrong messages or intentions, like how some characters misunderstood his help or gestures such that one turned to hate him or thought he was a teacher or friend.   Maybe that is a little off, but accumulatively, those little slips tend to add up to a general pattern of behavior with unintended consequences because of his lack of comprehension.  I can see he tends to think in black and white too which is partly why he goofs with some introductions.

Sousuke grew up in a rather difficult setting and it may or may not have either caused his extreme Autism like behaviors or just made what was already there far more prominent.  The source of most of the comedy from my top pick for humorous anime at least regarding season 3 of the series, is his social ineptness and his total lack of tactful responses because of how clueless he is to any and every signal or even literal explanation on how to behave socially.  The only things he understands are tactics, strategy, combat, weapons, and other military pursuits.  Anything else he has absolutely no clue about nor appears to have any remote interest in or even a desire to correct his ineptness or develop an interest to improve anything other than military related.  He is so socially defunct that even repeated complains and smacks by Chidori do little to improve his understanding.  Sometime he even takes big risks or runs into dangerous situations because his understanding of social cues or behaviors is so lacking.

Edit: True given his background, it could well be more ptsd related, but very unlikely.  He never seems to have issues with most of his combat experience and instead appears to use it more like a crutch to navigate a life he struggles to comprehend.  He applies his one size fits all military training and experience to everything.  Even if one had training, combat, or ptsd, it wouldn't necessarily exclude: an inability to understand language; intentions; sociall cues; appropriate behavior; his literal understanding of instructions; or his inability to corespondingly learn from his socio behavior mistakes.  He is hyper focused especially if given missions.  He takes things way too literally almost every time and often causes mayhem.  I'd dare say, he is one of the stronger cases for autism given the accumulation of information about him.

From the moment he appears on screen, especially after he crash lands, you just have to know this guy never met anyone in person who wasn't a boss or fellow soldier.  When he meets the non miitary humans, he literally shies away from them and hides in his own corner unsure what to do.  At first, he constantly asks his interactive computer for clues about human behaviors and socializing but the computer is almost as clueless as he is.  He is a little too calm, dispassionate, and logical compared to almost any other human.  Even his former commander had a bit more 'humanity' than Ledo does.  Perhaps even in the distant future, people still do not know how to properly deal with Autism?

It is hard to say for sure how autistic like this guy is or rather was before he met his friends, but he does exhibit typical behaviors such as his awkwardness around certain people and sometimes even in crowds.  He often does not seem to have a sense of reality or danger or proper placement or interaction with respect to cultures he finds himself in.  For the most part, he tends to have the vibe of a child.  Even among his friends he makes little impact with a small presence yet he has strong convictions and for things he likes alot he is a master, like cooking or studying books.  

Ai is extremely isolated and is rarely seen out and about anywhere.  She only talks to people that approach her through not so easy means to reach and a handful of people she knows and trusts.  Her lack of emotion and facial expressions are obvious.  It is no wonder her subordinates do much of the public and social related tasks as she does not appear to have much skill or desire in those respects.  

Tsutomu is one of the stronger more obvious candidates for autism.  His hobby of looking at ruined buildings alone is a good testament to that.  Even after he becomes something different his interaction with his new friends are evident of how awkward and socially inept he is.  Birdy, though is not much better but she has less of a sense of shyness and shame than him by far.  Tuto is without a doubt the most capable socially at least than any of Tsutomu's tight circle.  His meek and shoddy behavior in almost any social setting or his inability to comprehend others is pretty strong.  He even has repetitive habits and strong unique hobbies and knowledge.  When he talks, he is best at talking about one of his hobbies to the point of boring listeners.

Edit:  Some may doubt my analysis of Senkawa too.  Keep in mind, that certain events early on may have changed some of his more natural nature.  He had a narrow field of interest and was so hyper focused, that he wasn't even aware of what he stepped into until it was too late.  Sure he has friends, but that isn't unheard of and they shared some of his more unusually unique interests.  He showed a bit of sensitivity to some clothes he ended up wearing.  His interaction with Birdy's boss suggests at least a hint he isn't always appropriate in interaction with others.

Chiaki's blaringly loud ineptness at understanding others is so clear, you would find simple math harder to understand.  The fact she blames the person that saved her sister for what happened alone shows how incapable she is at grasping the understanding of others or even looking into facts themselves since she obviously doesn't talk to anyone else to find out for herself the truth of what happened to her sister.  She becomes obsessed with revenge almost like an addiction.  At one point when her life is in danger, she even hesitates to trust or accept help from others, proving she is a virtual null factor socially at her school.

He makes a grand show in public but later spends all his time as a virtual neet locked up in his room online.  He is only capable of talking to a handful of people but most of his talk is through online chat like contact so much so that he does not even realize he contacts one of his own friends from reality.  He has his own repetitive behaviors and obsessions such as shopping or eating noodles.

Tatsuya's father proves why Tatsuya has autism.  He is no better.  It is hard to say if he is worse because he does not appear in the novels or anime enough to fairly compare but it is pretty clear, he lacks social graces and tends to look and act a bit robotic when he is in public among people.  He even sends his second wife to interact with his own children at times rather than go himself.  If he can not even properly interact with them, just how badly does he have a social handicap?  

Tsubaki has a small meek voice just like her public presence.  She gives off the air of someone who lacks confidence and experience at least among friends.  During fights though, she often proves a more clear thinker than Blackstar so when her focus is not on things she can't handle well, her sharpness increases many fold.  

Shizuki has one friend before she meets Tatsuya, that alone indicates just how troubled she is.  Like Tatsuya and his father, she is nearly mechanical in her interactions.  She is smart and logical but struggles to grasp pretty much anything she has little or no strong interest in.  

Kazuya is good at what he does.  He clearly has been so obsessive with anything related to his special interests that he has become a master of them all but anything beyond that he is almost helpless.  You see plenty of examples of this when for example people such as children try to get his attention he looks to be at a loss.

For a guy who spent all his time avoiding people until he joins the group, it should come as no surprise that he might have tendencies like autism.  Any social interaction he had in the past were bad or dangerous so thus he grew to avoid or even hate them.  Most of the time after he left his previous home has been on the run out of the limelight and public eye.  But after the group, though he tries to be humble, his ineptness and lack of experience is pretty strong.

The reason Atsushi gets along so well with Kyouka maybe that both have autism.  They have similar backgrounds with low contact with others and what they have had didn't pan out well for them or the others.  

After the game world in Log Horizon became real, she found herself stuck in Hokkaido but she had no friends or contacts well at first.  Her lack of functionality in such a situation is a pretty good indicator she might be on the spectrum.  What she does after doesn't help demonstrating anything else either.  

During the technical competition just before the terror strike, George displays a bit of autism by discussing the technical details and qualties of the project Tatsuya worked on in great detail.  This is not something you might normally expect from another student, friendly or rival wise.  George never seems to do much on his own and when he visits Ichiha's house, he is harassed by the guy's younger sister but does not know how to deal with her.  We can know from reading that she has a romantic interest in him but we can also tell that either George does not realize this or simply has no idea how to handle it.  That is a very strong suggestion of an autism characteristic.  There are quite a few other things and incidents in both the novels and the anime that lead a strong suggestion, he has a form of autism or could certainly qualify for a diagnosis.

While Kei is not featured in the anime as much and is only a support character in the novels too, his very meek shy, sociallly awkward behavior certainly gives him a strong vibe of autism.  When they were on the bus to the 9 schools competition you almost got the feeling he was relieved to have a break from his girlfriend but not because he didn't like her but the sense of her crowding his space and him not getting how best to deal with it.  He works best on technical things in seculuded areas like labs or even with a like soul like Tatsuya, but looks more meek in more rowdy, noisy, or crowded situations.  

NEET.  Though that alone wouldn't show autism qualities, his ineptness in the new world doesn't help either.  Perhaps why he gets along much better with people with issues is an indicator?  In social settings, he tends to misread things badly that often come back to hurt him and or the group.  Even among his friends he frequently misunderstands or misreads social signals that turn out to make things worse.  He might seem sociable but to him this new world is basically like a game of the type he spent most of his time playing.  A few years ago I read there was a bit of an influx of autism cases in Japan which may or may not share curious timing with the autism boon.

Ok the best way to sum up her Autism is to say this, she read books to understand social concepts and fashion.  That alone virtually screams autism.  Even without that she speaks meekly and politely as if she is unsure how to do it and constantly asks questions or makes vague references to literay sources like as if saying 'isn't this how you do it?'.  Even after she is told she does it wrong, she has a hard time adjusting to 'new things' and changes.  Ya, she has such qualities.  They may not all look so clear but you can see both suble and strong blaring cllues she might very well have it.

Ryner loves isolation, solitude, books, and avoids people like the plague when he can.  Sure his powers and childhood tramatic experiences may have played a part but if he were truly an neurotypical, he probably could have gotten past those enough to get along better than he does.  Like people with Autism too, he has a great sensitivity to certain stimuli, like in his case, magic.  It is a shortcoming and an advantage.  Oversensitivity can make it hard to deal with things but that oversensitivy also makes it easier to sense things in greater depth or sooner than others.  It is one of those things typical in Autism.

Edit:  He has hyper focus when he's falsely detained and reads many books while tuning out his environment.  He's socially awkward as suggested by how Feris constantly chastised him for his lack of manners.

Honoka is a little more outgoing than her best friend, Shizuku but not by much.  She spends most of her time around her in her familiar spaces.  When she talks she is more meek than even Shizuku but less robotic like.  The nine schools competition showed how much she lacked confidence in anything she wasn't already super interested in or a master of.

Edit:  I could make a valid argument that she struggles so much with basics most NTs take for granted such as being aware of herself.  She likes Tatsuya but though she emits signals, she maybe just as bad at displaying them as Tatsuya is at reading them.  Her best friend for a long time seems to be the only one that can sense it until the dance after after nine sports contests.  

It’s said in episode 4 that nanny operators have emotional expression difficulties. She has a youthful underdeveloped mannerism despite a fair level of intellect. She struggles with socializing or even talking to anyone she isn’t at least familiar with and even those she is, it’s not a cake walk for her.

Edit:  I can make an argument that she has her special unique powers because she's overly sensitive to certain stimulation.  More subtle but common clues are like how she struggles at a part time job and isn't even sure what to do about getting one before that suggesting she lacks certain NT level skills and knowledge.  While one could argue the reason she suspects Layfon is deceptive might be due to body language it's more like it's because she senses more power in him then he presents publicly.

Being a 'NEET' or an 'OTAKU' may not guarantee a likiehood that one has Autism but it might at least increase the probability.  Suburu spent alot of time alone and hardly any even talking to people as if to say he is that bad at it.  When he travels to the new world he makes many mistakes, such as walking into a girls bathroom boldly, but this maybe because he did not know how to pay attention to social cues or observations at least respecting himself.  Oddly enough he is good at observing others but when he lectures on his knowledge or tactics he sounds just like a 'professeur' and we know one alt name for Autism say the Asperger's variation, is also known as 'little professeur's syndrome'.  You can look at how much trouble he has reading people especially girls cause it takes him so many times to get it.  It maybe only his power that gives him any idea how to circumvent his shortcomings in that way.

The fact he so easily became glued to a certain online game is enough to prove just how little he had going to keep him occupied otherwise.  The girl that forces him into the council clearly has her act together far more than he does as well as her communication skills.  He is a good thinker good at non interactive tasks and functions.  Just watching him gives you a good sensation, he might just have autism.

Edit:  I could say it was just shyness but, the addictive way he ends up focusing on a game is another important clue.  Asdies have been noted to have a higher than average susceptibility to addictive behavior and can get too focused on something.  (Like me when I'm so into something, hours and hours can pass and I'm too focused to realize I should eat, sleep, or do anything other than the task I'm locked on.)

He played all his games solo even when he entered SWO when his life was on the line.  He eventually joined a small one only to have his anxieties realized.  He has show awkwardness or inappropriate behaviors when socializing such as during raid parties.  His aloofness and solitary existance extended even more strongly into his real life.  Even after the events of SWO his 'autism' like qualities did not diminish by much.

Amendment:  Yes he might seem outgoing especially in the game but remember, he was more agoraphobic than you're average otaku or Asdie in real life at least before SAO in the earliest episodes.  My judgements are fair and logical and based on as much information as I can get access to plus some information might be weighted more important like, was this character outgoing in real life or a total hermit.  It wasn't just that though.  His early real life communication was eh and there are times even in the game where he misread cues or body language.  Also, these are only characters with a higher than average degree of chance they might have some form of autism or other PDDs.

I’ll Star by admitting, it might be less likely or even unlikely she is autistic yet she has shown some symptoms albeit not nearly as severe as Leon. She too is anti social, and though she shows mild signs of romantic interests, you can see her struggle to cope with or fully understand it or admit it. She contrasts nicely with Leon’s sister Chloe, who is very extroverted and social by comparison to about every character in this series. She also has few narrow interests and a hyper sense of concentration which is why she is actually slightly more capable than even Leon at controlling hyperdrive power. By contrast, the other character with super focus is actually very social and a playboy.

Teletha pretty much never leaves her 'comfortable' places like her work office and when she does she is like a fish out of water.  She is hopeless and clueless often making careless mistakes she would never even imagine possible if she were in her comfort zones.

Edit:  It's a bit subtle and I think at least one incident occurs in the comic ffummoffu season, but she did display a lack of understanding of social cues and reading signs.

Sure, his chances may not be certain but he's displayed some convincing symptoms.  He's awkward socially often misfiring on his interpretation of social cues.  He casually insults people without intent or realizing it then gets confused when he gets angry treatment. He can be focused enough to tune out all distractions. Anything out of his familiarity and comfort zone he gets a bit flustered and lost, such as eating at his regular table where the thought of eating elsewhere never entered his mind as a realistic alternative. He has essentially no friends that can be seen.  The only reason he interacts with the sisters, at least initially, is for a job. He even declares dating is merely a distraction.

His obsessions maybe to blame for his social ineptness but he also displays short attention span or attention that is too easily distracted even when he is supposed to be focused or his own life is at risk.  He pays too much attention to art and semmetry to the point it antagonizes even those closest to him and yet he never seems to realize it.  These are all prime and indictive qualities of autism.

Amendment:  Yes he is probably OCD, but OCD among those with autism is a common co-morbid disorder (co-morbid means people with an increased likelihood of getting other problems which autism does increase the chance of getting one or many other disorders).  He's a bit antisocial except to those he is already close to or knows well.  He has displayed some awkwardness around others he isn't as familiar with.  It's subtle clues like this that I pay attention to and determine the possibility this person might be an autism candidate if not at least some PDD.

Alex maybe somewhat debatable but he at least deserves honorable mention, if you will.  He rarely socializes, or talks to others save a few and mostly his closest aides.  There's a scene with Sophia where he appears to completely miss both her body language and subtle signs of something she seems to want from him, though if Alex noticed, he showed no signs of it.  He's exceptionally quiet in most situations and has his own forms of over focus obsessions such as strategy and navigation.  He often doesn't seem to get downtime for himself nor grasping it in others like at the port where he didn't socialize, drink, hangout, not try any of the functions or shops.